Bald eagle description

Instantly recognisable as the national emblem of the United States, the bald eagle (Haliaeetus leucocephalus) has long been a key symbol in the human cultures of the Americas. The second largest North American bird of prey after the Californian condor (2), the bald eagle is also the only eagle solely native to North America (5).

This majestic species is named for its conspicuous white head, with ‘bald’ coming from an old word meaning ‘white’. The bald eagle’s head is fully feathered, and contrasts strongly with the dark brown body and wings. The tail is also white, and the legs, eye and large beak are bright yellow (2)(3)(5)(6). The wings are long and broad, and the tail rounded. The female bald eagle is larger than the male, but otherwise similar in appearance (2)(3)(5). The call of this species is relatively weak, seeming rather inadequate for such a large bird (3).

The juvenile bald eagle can be recognised by its entirely dark brown plumage, mottled with white, and by the dark eye and beak. It takes at least five years to reach full adult plumage. Although similar in appearance to the golden eagle, Aquila chrysaetos, the juvenile bald eagle can be distinguished by its unfeathered lower legs (2)(3)(5)(6). Two subspecies of bald eagle are generally recognised, the northern Haliaeetus leucocephalus alascanus, and the smaller, southern H. l. leucocephalus. However, the boundaries between the two are not clearly defined (2)(3).

Related species

Bald eagle biology

The bald eagle is a powerful and opportunistic forager, feeding on a variety of prey including mammals, birds, reptiles, amphibians, crustaceans, carrion, and even garbage, although fish are preferred. Prey may be captured directly, scavenged, or stolen from other bald eagles or from other species. Birds, up to the size of geese, may be taken on the wing, while fish are usually taken from the water surface, or alternatively by wading into water, or by searching for dead or dying individuals (2)(3)(5). Cooperative hunting may also sometimes occur, one eagle flushing prey towards another (8). Bald eagles may gather in large groups at feeding sites, such as where salmon come to spawn, and often concentrate in large numbers of up to a thousand or more individuals at winter roosts (2)(3)(5).

The bald eagle is monogamous, and thought to pair for life, reinforcing the pair bond through spectacular, acrobatic flight displays that include the pair flying to a great height, locking the talons, and cartwheeling towards the ground, only breaking off at the last moment (2)(5). The breeding season of the bald eagle varies with location, ranging from April to August in Alaska and Canada, to November to March in southern USA (2)(3). Breeding pairs become highly territorial during this time (2). The nest is usually built in a large tree, or sometimes on the ground or a cliff. Both sexes help construct the nest, which is built with sticks and lined with grass, moss, seaweed or other vegetation. Material may be regularly added over many years, leading to one of the largest nests of all birds, the largest on record measuring a remarkable 2.9 metres across and over 6 metres deep (2)(3)(5). One to three white eggs are laid, and hatch after an incubation period of around 35 days. The young bald eagles fledge at around 75 to 80 days, but remain dependent on the adults for up to a further 6 weeks (2)(3). Young bald eagles do not start to breed until the fifth year, and are potentially long-lived, at up to 28 years in the wild and 36 years in captivity (2).

Bald eagle range

The bald eagle is found across Canada and the United States of America, and marginally into Mexico. Vagrant individuals have also been recorded from Belize, Bermuda, Puerto Rico and the US Virgin Islands, and even as far away as Ireland (2)(3)(7). Southern populations and northern coastal populations are largely resident, but inland Canadian and Alaskan birds may migrate south or to the coast during winter (2)(3).

Species with a similar range

Bald eagle habitat

This species typically breeds in forested areas next to large bodies of water, such as rivers, lakes, reservoirs, and coastal areas, although it may also be found in more arid regions in the south of the range. The bald eagle may spend the winter along the coast, along major river systems, or sometimes in waterless open country (2)(3)(5).

Bald eagle status

Bald eagle threats

Once common across much of North America, the bald eagle underwent a dramatic decline between the late 1700s and the 1960s as a result of intense hunting, habitat loss, and poisoning by pesticides (notably DDT), lead shot and other pollutants. In addition, DDT is believed to have caused widespread eggshell thinning and reproductive failure. Although still facing threats from human development, disturbance, pollution, and losses through collisions with powerlines and vehicles, a reduction in persecution of the bald eagle since the 1970s, together with improved habitat protection and a ban on DDT in 1972, have led to an impressive recovery for this species (2)(3)(7).

Bald eagle conservation

The bald eagle is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning international trade in the species should be carefully controlled (4), and is also on Appendix II of the Convention on Migratory Species (CMS or Bonn Convention), which aims to conserve migratory species throughout their range (9). In the United States, the species was listed for protection under the Bald Eagle Protection Act in 1940 (now the Bald and Golden Eagle Protection Act), and later under the Endangered Species Act of 1973, and various regional recovery plans were produced (2). However, the dramatic recovery in bald eagle numbers led to the species being removed from the federal list of threatened and endangered species in 2007, as it was no longer considered to need the protection of the Endangered Species Act (10).

Despite this, the bald eagle population will continue to be monitored, and still receives protection in the United States under the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act, both of which prohibit the killing, selling or harming of eagles, including the nests and eggs (10). The U.S. Fish and Wildlife Service have published a set of National Bald Eagle Management Guidelines (11), and a permit programme has recently been put in place to allow limited ‘take’ of bald eagles or their nests where the birds conflict with legal projects and activities (10)(12)(13). Further research has been recommended to assess the impact of increasing human development in bald eagle habitats, as well as the impact of forestry management practices (2), and the more vulnerable population in the Sonoran Desert, Arizona, which is still considered threatened (6), needs continued monitoring. However, many consider the recovery of this magnificent eagle to be one of North America’s most successful conservation stories (2), and a symbol of what can be achieved through cooperative conservation efforts (10).

Authentication

Glossary

Carrion

The flesh of a dead animal.

Crustaceans

Diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.

Incubation

The act of incubating eggs; that is, keeping them warm so that development is possible.

Monogamous

Having only one mate during a breeding season, or throughout the breeding life of a pair.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Territorial

An animal, a pair of animals or a colony that occupies and defends an area.

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